How much bhp will I gain for removing the cat. Also besides bhp does it make it sound louder? Am I best leaving it connected??

 

you will loose some a little on the bottom....but it will flow like crazy on the top end......you mite pick up about 2-3 bhp at the top end

 

I've never seen a dyno where a honda with a removed cat gained more than 5hp. I'm sure you choice of exhaust and headers will have some sway in this. To answer the first question, your car will get alot louder. IMO I wouldn't consider this a fair trade-off for a daily driver.

 

i just put a dc header on and i have a straight shot muffler tip, just baffles inside. it's pretty dam loud, dounds cool when u let off gas cruising kinda got a backfire sound to it. but i let my cat, and i recommend leaving yours. you need it for the back pressure, w/o it and other freeflowing exhaust you lose back pressure. and these small engines need it, unless your runing serios boost or some bg shot nitrius. you might gain some hp, but i'm willing to bet you lose torque.